Characterization of Disinfection By-product Precursors based on Hydrophobicity and Molecular Size

摘要

Natural organic matter (NOM) from five water sources was fractionated using XAD resins and ultrafiltration membranes into different hydrophobicity and molecular weight (MW) groups. The disinfection by-product (DBP) formation from each fraction during chlorination and chloramination was studied. In tests using chlorination, hydrophobic and high MW (e.g. >3kDa) precursors produced more trihalomethanes (THMs), trihaloacetic THAA) acids and unknown total organic halogen (UTOX) than corresponding transphilic, hydrophilic and low MW (e.g. <3kDa) precursors. However, the formation of THMs and THAA was similar among different fractions for a water with low humic content. Hydrophilic and MW<0.5k fractions gave the highest dihaloacetic acid yields. No significant difference was found for the dihaloacetic acid and UTOX formation among different fractions during chloramination. It appears that chloramination DBP precursors are more evenly distributed among NOM fractions. High pH favors the formation of THMs and HAAs over UTOX. Increasing pH also led to lower TOX formation for hydrophobic and high MW fractions, but had little impact on TOX yields from hydrophilic and low MW fraction. Bromine and iodine were found to be more reactive with hydrophilic and low MW fractions as measured by THM and HAA formation than their corresponding hydrophobic and high MW fractions. However, hydrophobic and high MW fractions produced more UTOX when reacting with bromine and iodine.